This invention relates an optical head for a magneto-optical memory, and more particularly to an optical head which detects, with a high sensitivity, the direction of polarization rotating through a very small angle in a relation corresponding to the direction of magnetization of a perpendicular magnetic thin film, so that information recorded on the perpendicular magnetic thin film can be reproduced with a high S/N ratio.
A magneto-optical disc memory is known as one of erasable (rewritable) optical information recording apparatus. An apparatus of this kind is described in, for example, N. Inamura and C. Ota; Japan J. Appl. Phys. 19 (1980) L731. According to the reported apparatus, information can be easily recorded and erased since the apparatus utilizes the light-induced thermo-magnetic effect. However, the reported apparatus, in which rotation, less than 1 degree, of the direction of polarization due to the magnetization is detected for reproducing recorded information, has had such a demerit that the quantity of reproduced signal light is very small, resulting in a low S/N ratio.